A variety of fan blades have been developed for use in automotive cooling systems. The fan blades operate to produce a flow of air over heat exchangers to cool the engine. Thus, the fan blades of an engine-cooling fan must be capable of withstanding the harsh temperature and chemical conditions present in an engine environment. Also, it is important that engine cooling fans be formed with minimal mass, since fan mass is generally inversely related to the operating life of other operationally related engine fan drive components, such as bearings, the water pump, and the like. It is, therefore, desired that engine cooling fan blades be designed to be both chemically and mechanically durable materials, as well as being lightweight as possible.
The construction of typical prior art cooling fans has required a compromise between the physical durability and the overall weight of the fans. Prior art fan blades have traditionally been made from durable structural metallic materials, such as heavy gauge steel or aluminum. As shown in FIG. 1, a prior art metal spider fan 10, which is a metal disk or hub 12 from which a plurality of twisted legs 14a extend, is provided to which a plurality of fan blades 30 are attached. The legs 14a are twisted to provide an appropriate angular displacement for the blades 30, which are fastened to the spider legs 14a, typically by bolts, welds, or rivets. Due to the forces experienced by the spider legs 14a, the spider legs typically require a stress relieving treatment as a step in the spider manufacturing process, to minimize the introduction of weaknesses in the form of excess embrittlement through strain hardening, small cracks or other imperfections inherent in the spider leg twist operation that could impair the structural integrity of the fan and thus shorten the operating life of the fan.
Certain other prior art fan blades, as shown in FIG. 2, have been constructed of thermoplastic materials, such as injection-molded nylon. These prior art blades include short reinforcing fibers dispersed in a thermoplastic matrix, and are used to form entire, unitarily molded fan assemblies (i.e., hubs with multiple contiguously formed fan blades extending therefrom) via a high-pressure injection molding process. These fans, while lighter than comparably strong metal fan assemblies, still suffer from the drawbacks of requiring relatively expensive molds for use in costly injection molding processes. Moreover, in order to alter the geometry of the fan blades, an entire new fan must be molded, thereby requiring a new, separate mold.
Thus, there remains a need for a high-strength, lightweight and relatively low cost fan blade system. The present invention addresses this need.